A thermal desorption type sample introduction device which introduces samples into an analytical device such as a gas chromatograph is a device which heats a sample tube filled with an adsorbent and solid sample in order to volatilize the adsorbed components, and introduces them through a transfer line into the column of the gas chromatograph.
In this sort of sample introduction device, if the sample tube is connected directly to the column to introduce the sample components into the column, since the volume of the adsorbent with which the sample column is filled is large while the flow rate inside the column is low, there is the problem that it takes a long time for all the components to pass through the column, and the detection peak bandwidth becomes wide. Thus, a method is employed whereby a trap including a tube filled with a small amount of adsorbent is provided inside the device, and a gas containing the sample components desorbed from the sample tube is passed through the cooled trap to cause adsorption of the components onto the trap, after which the trap is heated to again desorb the sample components and introduce them into the analytical column.
There are devices in which, when introducing the sample components desorbed from the trap into the analytical column, in order to narrow the detection peak bandwidth, only a portion of the gas containing the sample components desorbed from the trap is introduced into the analytical column. Such devices include devices wherein the channels are configured so as to return the split gas which was not introduced into the analytical column to the sample tube side, making it possible to recapture the sample components in the sample tube and reuse them for the next analysis (see Patent Literature 1).
An example of the channel configuration of a sample introduction device for a gas chromatograph including a function of performing recapture of samples will be explained using FIGS. 5A and 5B.
A carrier gas channel 112 for introducing carrier gas is provided. The carrier gas channel 112 branches into channel 114 and channel 118. One of the channels 114 which branches from the carrier gas channel 112 branches further into sample channel 106 and recaptured gas discharge channel 122. A stop valve 116 is provided in channel 114, allowing the channel to be opened and closed. Sample channel 106 is connected to one port of rotary valve 102. Furthermore, a sample tube 104 is arranged in sample channel 106. The sample tube 104 can be heated or cooled by a temperature regulation mechanism 105. A stop valve 124 is arranged in recaptured gas discharge channel 122.
One end of trap channel 110 and one end of sample introduction channel 132 are connected to the other port of rotary valve 102. A captured gas discharge channel 136 and sample introduction gas supply channel 126 are connected to the other end of trap channel 110. The other end of sample introduction channel 132 is connected to a joint 130. A trap column 108 is arranged in the trap channel 110. The trap column 108 can be heated or cooled by a temperature regulation mechanism 109. A stop valve 138 is arranged in captured gas discharge channel 136.
The other channel 118 branched from the carrier gas channel 112 is connected to one port of a three-way valve 120. Channel 128, which leads to sample introduction gas supply channel 126 and joint 130, is connected to the two remaining ports of the three-way valve. Channel 118 is switched and connected to one of sample introduction gas supply channel 126 or channel 128 by the three-way valve. Analysis channel 134 is also connected to joint 130.
Rotary valve 102 can be placed into a state in which sample channel 106 and trap channel 110 are connected (the state of FIG. 5A), and with a different timing, can be placed into a state in which sample channel 106, trap channel 110 and sample introduction channel 132 are connected (the state of FIG. 5B).
The thick line in FIG. 5A is the path along which the carrier gas flows during the process of capturing the sample from sample tube 104 in trap column 108 (hereinafter, the trap capture process). The channels are configured such that, in the trap capture process, a portion of the carrier gas from the carrier gas channel 112 flows through channel 114-sample channel 104-trap channel 110-capture gas discharge channel 136, and the rest of the carrier gas flows through channel 118-channel 128-analysis channel 134. Here, the sample tube 104 is heated to a set temperature by temperature regulation mechanism 105, and the trap column 108 is cooled to a set temperature by temperature regulation mechanism 109. As a result, the sample from the sample tube 104 is desorbed and flows together with the carrier gas, and that sample is captured in trap column 108.
The thick line in FIG. 5B is the path along which the carrier gas flows during the process in which a portion of the sample captured in trap column 108 is introduced into the analytical column and the rest of the sample is recaptured in the sample tube 104 (the sample introduction and recapture process). In the sample introduction and recapture process, the carrier gas from the carrier gas channel 112 passes through channel 118 and channel 126 and flows through trap channel 110. Here, the trap column 110 is heated to a set temperature by temperature regulation mechanism 109, and sample tube 104 is cooled to a set temperature by the temperature regulation mechanism. The desorbed sample from the trap column 110 flows along with carrier gas to rotary valve 102. The rotary valve 102 is switched to a state in which sample channel 106, trap channel 110 and sample introduction channel 132 are connected. Gas containing the sample desorbed from trap column 110 is split via joint 130 to the sample introduction channel 132 side connected to analysis channel 134 and to the sample channel 106 side. As a result, a portion of the sample desorbed from the trap column 108 passes through analysis channel 134 and is guided to the analytical column of the chromatograph, and the rest of the sample is recaptured in the sample tube 104.